The present invention relates to a driver circuit. Specifically, the invention relates to a driver circuit that is preferably applicable for reducing the losses and noises of an insulated gate power device and for improving the driving performances thereof.
In semiconductor electric power converters, insulated gate power devices such as an insulated gate bipolar transistor (hereinafter referred to as an “IGBT”) and a power MOSFET are used. Some conventional driver circuits for driving the insulated gate power devices are formed of an inverter.
FIG. 6, for example, is a circuit diagram briefly describing the structure of a conventional driver circuit. In FIG. 6, the conventional driver circuit includes P-channel field-effect transistor 41 and N-channel field-effect transistor 42 connected in series to each other. The source of P-channel field-effect transistor 41 is connected to a power supply voltage Vcc. The source of N-channel field-effect transistor 42 is connected to the ground potential. The drain of P-channel field-effect transistor 41 and the drain of N-channel field-effect transistor 42 are connected commonly to the gate of IGBT 43. A driving signal is fed commonly to the gate of P-channel field-effect transistor 41 and the gate of N-channel field-effect transistor 42. A signal that shifts between a low level and a high level may be used for the driving signal. The low level may be set at 0 V and the high level at the power supply voltage Vcc with no problem.
In order to turn on IGBT 43, the driving signal is set at a low level. As the driving signal is set at the low level, P-channel field-effect transistor 41 is turned on and N-channel field-effect transistor 42 is turned off. As transistor 41 is turned on and transistor 42 is turned off, the power supply voltage Vcc is applied to the gate of IGBT 43 via P-channel field-effect transistor 41. As the power supply voltage Vcc is applied to the gate of IGBT 43, a charging current flows to the gate of IGBT 43. As the charging current that flows to the gate of IGBT 43 raises the gate potential of IGBT 43, IGBT 43 is brought into a conductive state.
In order to turn off IGBT 43, the driving signal is set at the high level. As the driving signal is set at the high level, P-channel field-effect transistor 41 is turned off and N-channel field-effect transistor 42 is turned on. As transistor 41 is turned off and transistor 42 is turned on, the ground potential is applied to the gate of IGBT 43 via N-channel field-effect transistor 42. As the ground potential is applied to the gate of IGBT 43, electric charges are discharged from the gate of IGBT 43. As the electric charges are discharged from the gate of IGBT 43, the gate potential of IGBT 43 falls, thereby bringing IGBT 43 into a nonconductive state. In driving IGBT 43, the on-resistance of P-channel field-effect transistor 41 is used for turning on IGBT 43 and the on-resistance of N-channel field-effect transistor 42 is used for turning off IGBT 43, respectively.
U.S. Pat. No. 6,459,324 describes the prior art technique thereof disclosed by the U.S. Pat. No. 6,208,185. The prior art technique divides the turn-on period into an early stage I, a middle stage II and a late stage III. The gate of IGBT 43 is driven with adjusted driving capabilities in the stages I through III as described below to reduce the losses and noises caused in IGBT 43 and to improve the driving performances of the driver circuit.                Stage I: The gate of IGBT 43 is driven with a high driving capability (with a large output current from the driver circuit) to minimize the delay caused in the gate voltage rise.        Stage II: The gate of IGBT 43 is driven with a reduced driving capability to reduce the turn-on gradient (dlc/dt) of the drain current of IGBT 43 and to reduce the noises caused in IGBT 43.        Stage III: The gate of IGBT 43 is driven with a high driving capability to reduce the losses caused in IGBT 43.        
However, in intelligent power modules (hereinafter referred to as “IPM's”), an insulated gate power device such as IGBT 43 and the driver circuit thereof are mounted on a same module. Usually, the insulated gate power device is guaranteed to operate at the maximum temperature of 150□. Therefore, when an insulated gate power device and the driver circuit thereof are mounted on the common module, the driver circuit positioned in the vicinity of the insulated gate power device is in a thermally severe environment. Moreover, the on-resistance of P-channel field-effect transistor 41 and the on-resistance of N-channel field-effect transistor 42 tend to be higher at a higher temperature higher than at the room temperature.
Due to the reasons described above, the gate of IGBT 43 is charged at a more reduced rate at a high temperature than at the room temperature by the driving scheme that drives IGBT 43 using the on-resistance of P-channel field-effect transistor 41 and the on-resistance of N-channel field-effect transistor 42 as shown in FIG. 6. As a result, a sharp voltage change (the change of the voltage between the collector and emitter of IGBT 43) is prevented from occurring and the noises caused by the voltage change are reduced. On the other hand, the period necessary for the turn-on of IGBT 43 is elongated and losses are increased. If the gate drive is designed optimally to minimize the losses caused at a high temperature, the gate of IGBT 43 will be charged too fast at the room temperature, a sharp voltage change will be caused, and noises will be increased.
In the scheme described in FIG. 6, a tradeoff exists between the noises and losses. Therefore, it is necessary to analyze the noises and losses at the room temperature and at a high temperature and to design a gate drive based on the analyses at the room temperature and at the high temperature. Therefore, many man-hours are necessary for the gate drive design.
For adjusting the driving capability in the turn-on stages I through III by the method disclosed in U.S. Pat. No. 6,459,324, it is necessary to connect a series circuit of a capacitor and a resistor to the gate of IGBT 43 driven by a driver circuit. Therefore, the number of component parts and the substrate area are increased, further causing manufacturing cost increase.
In view of the forgoing, it would be desirable to provide a driver circuit that makes it possible to reduce the losses and noises of a power device and to improve the driving performances thereof without connecting a series circuit, including a capacitor and a resistor, to the gate of the power device thereof.